1. Field of the Invention
The present invention relates to turbine combustors, and more particularly to a biomass fueled turbine combustor utilized in conjunction with a biomass fueled pressurized gasifier.
2. Description of the Related Art
Efficient use of waste products is a mandate from our waste conscious society. Agricultural waste products and other cellulosic waste material such as wood waste, also known as biomass, are reusable natural resources which can be utilized as a source of energy production. Biomass is converted to a low British Thermal Unit (BTU) gas which can be converted into a useful fuel for a gas turbine engine. However, standard turbine combustors are not suitable for combustion of low BTU gas because of among other factors, flame stability problems. The increased use of biomass as a fuel source has been limited by the inability to fully utilize biomass as a fuel in conjunction with power generators.
The nitrogen content of biomass fuel creates additional difficulties that are less of a problem with the combustion of natural gas. The nitrogen content may result in high nitrogen oxide (NOx) emissions in the exhaust gases which are pollutants deleterious to human health and agricultural production. Nitrogen dioxide (NO2) and nitrogen oxide (NO) pose the greatest potential harm to human health and agricultural production, and their formation in the combustion of biomass fuel must be limited in order to more fully utilize biomass fuel as an energy source. Nitrogen oxide formation in fuel is a consequence of organically bound nitrogen converted to ammonia radicals (*NH3) and subsequently converted to nitrogen oxide (NO) through reaction with oxygen (O2). The inventive minds of the biomass energy industry have set forth the principals of how to achieve combustion of low BTU gas with limited formation of nitrogen oxides (NO). The principals include staged combustion, in which the oxygen supply is limited in the rich (greater than stoichiometric) burn zone, and the remaining required oxygen is supplied in the lean (less than stoichiometric) burn zone. Another principal to limit nitrogen oxide formation is aerodynamic recirculation of heat and re-radiation from refractory surfaces during combustion of the low BTU gas in order to achieve flame stabilization.
Another problem associated with burning low BTU gas derived from biomass is tar buildup. Tar buildup occurs when produced gas is cooled before entering the combustion chamber, resulting in tar buildup around valves and other places. This occurs even with tar cleanup devices added to the system and results in heavy maintenance to keep the units operating. If the fuel gas could be injected into the combustion chamber hot, which would also retain its sensible heat content, then tar buildup would be reduced and thermal efficiency improved for a biomass fueled integrated gasifier/gas turbine power plant.
The inventive minds of the gas turbine combustor industry have brought forth several inventions to limit nitrogen oxide formation in combustors. However, these combustors have not been directed to burning low BTU gas derived from biomass.
DeCorso, U.S. Pat. No. 4,787,208, discloses a combustor for inhibiting NOx formation through limiting oxygen in a rich burn zone, and providing a low combustion temperature in the lean burn zone. In this manner, nitrogen molecules cannot compete with carbon and hydrogen for limited amount of oxygen molecules.
Joshi et al, U.S. Pat. No. 4,912,931, discloses a staged low NOx gas turbine combustor having a lining for the interior wall of the primary combustion chamber composed of a porous fibrous refractory thermally insulative material with a layer composed of compliant fibrous refractory thermally insulative material between the lining and the shell of the primary combustion chamber, the invention directed towards providing a combustor which burns heavy crude oil while maintaining low NOx emissions.
Joshi et al, U.S. Pat. No. 4,928,481, discloses a staged low NOx gas premix gas turbine combustor having first and second stage regions in which a lean premixture of fuel and compressed air are introduced into the first stage producing a first stream of combustion, and a second premixture of fuel and compressed air are introduced into the second stage producing a second stream of combustion which collides with the first stream producing a divergent intensely turbulent flow.